1. Field of the Invention
The present invention relates generally to a wide angle zoom lens system having a high variation ratio, and more particularly, to a wide angle zoom lens system having a zooming range between a wide angle and a semi-telescopic angle, with a zoom ratio of approximately 2.3 to 3.0 times.
2. Description of the Prior Art
For example, in a 35 mm camera having a film frame of 36.times.24 mm, the wide angle range is in range of focal lengths between 28 mm and 35 mm. In respect to this wide angle range, Japanese patent application Ser. No. 52-55046 discloses a lens system having a high variation ratio which provides such a zooming range. Japanese patent application Ser. No. 52-55046 discloses the so-called two-lens group-type zoom lens system having a front lens group which exhibits a negative lens power, and a rear lens group which exhibits a positive lens power. The front lens group and the rear lens group are independently moved axial with respect to each other.
In such a two-lens group-type zoom lens system, the following inherent disadvantages are present. Because the zoom variation effect depends only on the rear lens group, the amount of zoom movement of the front and rear lens groups tends to be long in order to maintain the high zoom variation ratio. In addition, the aperture of the lens most adjacent the object tends to be large, and the variation of the luminous flux position is very substantial during zooming, especially in the front lens group. Moreover, the angle defined by the luminous flux and each lens element tends to be varied in proportion to the zoom variation ratio in the rear lens group.
In order to eliminate the above-mentioned deficiencies, each lens group and each lens thereof must have a high lens power. The high lens power, however, requires that the aberration variations be tightly controlled due to the inclination of each lens element. Because at the narrow angle end the variation of the width of the luminous flux incidental to the front lens group increases in proportion to the zoom variation ratio, the conventional two-lens group type zoom lens system requires tight control in order to offset the aberrations, that is, a delicate lens. Thus, the conventional two-lens group type zoom lens system is a delicate lens system that is difficult to operate so as to produce optimum optical results.